A fabrication process of a semiconductor device for forming a layered structure of an integrated circuit on the surface of a substrate, for example, a semiconductor wafer (hereinafter, referred to as a wafer), includes a liquid processing process for removing fine particles or a natural oxide film on the surface of the wafer by a chemical liquid.
A single-wafer type spin washing apparatus, as a liquid processing apparatus used for the liquid processing process above, removes particles or a natural oxide film on the surface of the wafer by rotating the wafer while supplying an alkaline or acidic liquid to the surface of the wafer by a nozzle. In this case, the liquid remained on the surface of the wafer is removed through spin-drying by the rotation of the wafer, after a rinsing process is performed by pure water.
However, as a semiconductor device is highly integrated, so-called a pattern collapse has become serious in the process of removing such a liquid. The pattern collapse indicates a phenomenon where in the drying of the liquid remained on the surface of the wafer, when the liquid remained on the left and right sides of a projection portion of unevenness forming a pattern is non-uniformly dried, the balance between leftward and rightward surface tensions on the projection portion is collapsed, and thereby the projection portion is collapsed in the direction of the side that the liquid remains in a larger amount.
As a method for removing the liquid remained on the surface of a wafer and inhibiting such pattern collapse, there has been known a drying method using a supercritical-state fluid (supercritical fluid). A supercritical fluid has a lower viscosity, compared to a liquid, and also a high liquid-solubility. Besides, in the supercritical fluid, there exists no interface between liquid and gas. Accordingly, when a wafer with a chemical liquid remained thereon comes in contact with the supercritical fluid and the chemical liquid on a wafer surface is dissolved in the supercritical fluid, it is possible to dry the chemical liquid without an influence of surface tension.
Herein, the supercritical state requires a certain condition, such as high temperature and high pressure. Thus, after being washed and rinsed by a chemical liquid, a wafer with the liquid remained thereon is carried to a supercritical processing device for supercritical drying. However, when the liquid on a wafer surface is naturally dried during the carrying of the wafer from a liquid processing apparatus to the supercritical processing device, pattern collapse may occur by a process of the natural drying.
As a technology for carrying a wafer while inhibiting the surface of the wafer from being naturally dried, Japanese Laid-Open Patent Publication HEI. No. 7-17628 (see [0011] and FIG. 1) and Japanese Registered Patent Publication No. 3933507 (see [0030] and FIG. 3b) disclose wafer carrying methods, in which a cover-type member covers the surface of a wafer, and a wafer is carried in a state where a space between the cover-type member and the wafer is filled with a liquid.
In the method disclosed in Japanese Laid-Open Patent Publication HEI No. 7-17628, the wafer can be adhesively supported by the liquid filled between the cover-type member and the wafer, and can be carried without the support on the lower surface of the wafer. However, the liquid is likely to overflow from the space between the wafer and the cover-type member. Meanwhile, in the method disclosed in Japanese Registered Patent Publication No. 3933507, although a receiving plate for receiving the liquid overflowing downward from the wafer is provided, the upper and lower sides of the wafer are required to be covered from both sides. This complicates the configuration of an apparatus or the control on the operation, and causes a reduction of throughput, due to a prolonged carrying time.